Research Reports

Improving the Cost Effectiveness of Highway Construction Site Erosion and Pollution Control

Description:
A comprehensive two-phase effort was conducted to improve the cost-effectiveness of erosion and pollution control at highway construction sites. This report covers both phases of the research. The initial work included laboratory model-scale testing of sedimentation pond designs and field monitoring of ponds to establish their effectiveness in pollutant removal. The laboratory models demonstrated that the following design features in concert maximize actual water residence time to promote sedimentation: (1) length/width ratio of 5:1; (2) series arrangement of two chambers rather than a single pond of equivalent size and shape; and (3) using a perforated riser outlet. To verify these results in a full-scale application, a sedimentation pond was designed according to the laboratory findings, constructed in a highway right-of-way, and monitored for pollution control performance. Another sedimentation pond without these design features was tested for comparison. A second pond based on the laboratory results was tested later. Monitoring consisted of flow measurement and water runoff composite sampling at pond inlets and outlets. Samples were analyzed for solids, metals, phosphorus, and organic content. Costs were also established for these ponds. Results demonstrated that the ponds designed according to the laboratory findings were both more efficient in pollutant removals and less costly (per unit area served) than the pond to which they were compared. The later phase of the work concentrated most on testing the ability of various mulches, blankets, and chemical products to prevent erosion on test slopes, as well as on the ability of silt fencing to contain erosion from such slopes. Runoff samples were collected at the bottoms of the slopes and analyzed as in the pond studies, and costs were again established. Overall, wood fiber mulch accompanied by grass seeding was the most cost-effective slope covering. This report is issued in conjunction with an erosion and pollution control manual, which is designed to implement the findings in highway construction practice.